Courtois only lasted 45 minutes against Manchester City in the second leg of the Champions League round of 16 as Madrid beat the Premier League side 2-1 on Tuesday night.
Manager Álvaro Arbeloa claimed it was a precautionary substitution even though Courtois “wanted to continue” the game as Madrid booked their place in the Quarter Final.
Now, Madrid have released a statement after reviewing the extent of the injury which is likely to rule out the Belgian star for a number of weeks.
“Following tests carried out today on our player Thibaut Courtois by the Real Madrid Medical Services, he has been diagnosed with a muscular injury in the rectus femoris of his right quadriceps. Awaiting further evaluation.”
Atlético Madrid are headed to the Bernabéu on Sunday evening for a Madrid derby where Courtois will be absent.
The Spanish giants also face Bayern Munich in the next round of the Champions League in a few weeks time and reports claim the shot stopper may not be ready to start against the German giants.
Ukraine goalkeeper Andriy Lunin will step into the side for the time being as Arbeloa tries to deal with an already injury riddled side.